14 April 2011

Hot pink climate no laughing matter

Do climate scientists have a sense of humour? In the case of James Hansen, head of the Goddard Institute for Space Science (GISS) at NASA, and perhaps the world’s best known climate researcher, the answer appears to be yes.

Hansen’s team regularly publish global maps of temperature changes, and in the most recent the warming in the Arctic was sufficient to run off the existing colour-graded scale. Needing to add a tone, their choice of colour was hot pink.

“Hot” pink indeed. That colour designated parts of northern Canada, Greenland and the surrounding ocean that this northern winter were more than 6 degrees Celsius warmer than the baseline temperature average for the period of 1951-1980, and 7 to 9 degrees Celsius above average over the Chukchi Sea. This is extraordinary, with consequences for our understanding of how fast the climate system is changing, and for climate mitigation policy.

The laws of physics determine that warming will be greater at the poles by a factor of two-to-three times the global average, but the impacts are far beyond those scientists anticipated only a decade ago. Much of the Arctic Ocean is cover by a thin layer of floating sea-ice, approximately the area of Australia, and reducing in summer. But in the northern summer of 2007 it dropped precipitously (as one leading glaciologist exclaimed that it was “melting a hundred years ahead of schedule”) and the pattern is heading downward.

There are a number of consequences:

Weather patterns across the northern hemisphere are being affected, with a likely long-term fall in rainfall across much of the western United States and, ironically, more bleak winters. This northern winter, the sea-ice extent was the equal lowest in the satellite record with more ocean than usual free of ice, and extreme weather consequences. Ice-free water warms the air above, creating energy that likely pushed Arctic cold air south to produce a bitter winter in much of north America and northern Europe and Asia. And that after a 2010 summer that was exceptionally warm in eastern Europe and large parts of Russia that caused adverse impacts exceeding the amplitude and spatial extent of the previous hottest summer of 2003. Welcome to a world of more weather extremes.

As the sea-ice diminishes, it is also becoming thinner and so more vulnerable to further loss. Whilst in previous times it was thought that summer sea-ice would survive to 2100, a new regional climate model just developed for the Arctic now suggests produces a "best guess" date of 2016 for the total loss of summer sea-ice. This work, led by Wieslaw Maslowski, is not be trifled with. As a researcher at the US Naval Postgraduate School, Maslowski had unparalleled access to decades of data on Arctic ice thickness accumulated by military submarines in their stealthy sub-surface mapping of the Arctic during the Cold War, and his expertise is second to none. As heat-reflecting ice is replaced by dark ocean, vast amounts of heat will be absorbed into the Arctic, with consequences for the large ice sheet that covers most of Greenland. With summer sea-ice gone and heat pouring in, many Arctic experts think that Greenland would certainly pass its tipping point for large ice mass loss, and the Greenland ice sheet contains enough water for a 6-7 metres sea-level rise.

There are also concerns that a large build-up of fresh water in the Arctic could spell trouble for northern Europe and Britain if it suddenly flowed into the north Atlantic and affected the warm Gulf Stream that keeps the region mild in winter and cool in summer.

Most worrying are the state of vast carbon stores, frozen in the northern permafrost. Containing about 1.5 trillion tonnes of carbon (twice that in the atmosphere), new predictions suggest that as soon as 2020 carbon emissions from melting permafrost could be close to a billion tonnes a year. They find that this positive permafrost carbon feedback will “will change the Arctic from a carbon sink to a source after the mid-2020s and is strong enough to cancel 42–88% of the total global land sink.” Research suggests that warming of 8-10 degrees in Siberia would be enough to trigger the unstoppable release of most of the region’s stored carbon in as little as a hundred years, which it was thought would not happen till global average warming hit 3 degrees or more. But Hansen’s small hot pink band is another sign that Arctic amplification may be at the high end of the possibilities, and that flash of pink may be a code red alert.

As Hansen found recently, at the current temperature there is no “cushion” left to avoid dangerous climate change, and that the Australian government target goals “… of limiting human-made warming to 2 degrees and carbon dioxide to 450 ppm are prescriptions for disaster”. New evidence from the Arctic only confirms that sobering conclusion.